Coating thickness control and fluid handling

ABSTRACT

Continuous strip is hot-dip coated and passed between coating control nozzles from which gaseous fluid is projected to form gaseous barriers which wipe excess coating material back into the melt. The width of the gas outlet slot in each nozzle is controlled by thermally expanding at least a portion of the walls of the slot, thereby constricting the slot and thus controlling the flow of gas through the slot, thereby in turn controlling the wiping action of the gaseous barrier on the coating and thus controlling coating thickness. The width of the slot can be selectively controlled at increments in a direction along the length of the slot by a variety of heating means, to produce desired coating thickness at each increment across the width of the strip. The heating means is under remote control and the control system can include structure for displaying slot width and can include automatic control structure. At least a portion of the walls of the slot is of material having a high coefficient of thermal expansion, to enhance the effect of heating. The width of the slot can also be adjusted by cooling at least a portion of the walls of the slot, thereby thermally contracting the walls of the slot and thus enlarging the slot. Cooling can be used to make rapid changes in slot width, to dislodge foreign matter from the slot, to aid the heating means in production of a large temperature differential between intermediate and end portions of the slot, or for other purpose.

United States Patent [191 Atkinson [111 3,841,557 Oct. 15,]1974 COATINGTHICKNESS CONTROL AND FLUID HANDLING [75] Inventor: Edward S. Atkinson,Michigan City,

Ind.

[73] Assignee: National Steel Corporation,

Pittsburgh, Pa.

22 Filed: on. 6, 1972 21 Appl. No.: 295,740

[52] U.S. Cl 239/11, 138/46, 239/597 [51] lint. Cl F23d 15/00 [58] Fieldof Search 239/11, 13, 133, 135, 597,

Primary Examiner-M. Henson Wood, Jr. Assistant ExaminerMichael Y. MarAttorney, Agent, or FirmShanley and ONeill [57] ABSTRACT Continuousstrip is hot-dip coated and passed between coating control nozzles fromwhich gaseous fluid is projected to form gaseous barriers which wipeexcess coating material back into the melt. The width of the gas outletslot in each nozzle is controlled by thermally expanding at least aportion of the walls of the slot, thereby constricting the slot and thuscontrolling the flow of gas through the slot, thereby in turncontrolling the wiping action of the gaseous barrier on the coating andthus controlling coating thickness. The width of the slot can beselectively controlled at increments in a direction along the length ofthe slot by a variety of heating means, to produce desired coatingthickness at each increment across the width of the strip. The heatingmeans is under remote control and the control system can includestructure for displaying slot width and can include automatic controlstructure. At least a portion of the walls of the slot is of materialhaving a high coefficient of thermal expansion, to enhance the effect ofheating. The width of the slot can also be adjusted by cooling at leasta portion of the walls of the slot, thereby thermally contracting thewalls of the slot and thus enlarging the slot. Cooling can be used tomake rapid changes in slot width, to dislodge foreign matter from theslot, to aid the heating means in production of a large temperaturedifferential between intermediate and end portions of the slot, or forother purpose 13 Claims, 13 Drawing Figures Pmmm WW1 3.841. .557

sum 1 ar 4 v IA 0000000000000oooocoooooooooooooo000000oooooooooooooooooooo fi COATINGTHICKNESS CONTROL AND FLUID HANDLING BACKGROUND OF THE INVENTION Arevolutionary coating control system for galvanizing has recently comeinto use. In this sytem, which is described in Mayhew US. Pat. No.3,499,418, the thickness of a hot-dip zinc coating is controlled by jetsof gas issuing from coating control nozzles between which steel strip ispassed with the coating still in molten condition. The gas jets, whichextend transversely across the strip, form gaseous barriers which wipeexcess coating metal back into the zinc pot without contact of themolten coating by any mechanical device. This system produces improvedsurface and other qualities in the galvanized product.

In operation of such gaseous barrier coating weight control lines, thereis a problem in that it is difficult to maintain the thickness of thecoating at desired values at all increments across the width of thestrip, particularly at the strip edges where there is a tendency for thecoating to be thicker than desired. This so-called heavy edge isdisadvantageous, inter alia, in producing spooled coils which in turnproduce wavy edges in the strip upon uncoiling. Such wavy or pie-crustedges render the strip commercially unacceptable.

It is known that changing the width of the gas outlet slot in a coatingcontrol nozzle can change the thickness of the coating, all otheroperating variables being equal. Prior proposals for changing the widthof the gas outlet slot to control coating thickness have included theuse of removable shims or inserts to form at least one wall of the gasoutlet slot so that, by interchanging the shims with shims of differentsizes, the width of the gas outlet slot can be changed. The prior artproposals have also included the use of adjusting screws or bolts towarp the walls of the slot towards one another, or to releasably hold awall of the slot in any of a plurality of manually set positions whichprovide different slot widths."

Such slot-width control techniques are deficient in a number ofrespects. They are slow and require an excessive amount of labor to makethe adjustment. And, interruption of what would otherwise be acontinuous process for work on the nozzle is usually required, therebycausing expensive downtime on the coating line. Also, the labor requiredon the nozzle is a hot and unsafe type of work because of proximity tomolten metal and other high-temperature materials.

These deficiencies of the prior art are overcome by the presentinvention, which makes it possible to control the width of the gasoutlet means instantaneously, with a minimum of hand labor, withoutinterruption of the coating process, and with safety and comfort.

Other advantages of the invention will appear from the followingdetailed description which, in connection with the accompanyingdrawings, discloses several embodiments of the invention for purposes ofillustration only and not for defining the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates acoating system embodying principles of the invention.

FIG. 2 is a left side view of structure illustrated in FIG. 1.

FIG. 3 is an enlarged view taken on the section planes designated byline 3-3 of FIG. 2.

FIG. 4 is a view on the cross-section plane indicated by line 44 in FIG.3.

FIG. 5 is a view of nozzle and cooling details, taken in part on thesection planes designated by line 5-5 in FIG. 3.

FIG. 6 is a view on the section plane designated by line 6-6 in FIG. 5.

FIG. 7 is another view of nozzle and cooling details, taken in part onthe planes indicated by line 7-7 in FIG. 3.

FIG. 8 schematically illustrates operation of heating and controldetails of the system of FIG. 1.

FIG. 9 schematically illustrates another form of nozzle heating andcooling structure embodying principles of the invention.

FIG. 10 schematically illustrates another form of nozzle heatingstructure embodying principles of the invention.

FIG. 1] schematically illustrates still another form of nozzle heatingstructure embodying principles of the invention.

FIG. 12 schematically illustrates another form of heating control andcooling structure embodying principles of the invention.

FIG. 13 illustrates another form of heating element which can be used inthe structure of FIG. 1.

Reference numerals with the letter suffix A, B, C, etc. denote elementswhich are similar to the elements designated by the correspondingreference numerals having no letter suffix.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS With reference toFIGS. 1 and 2, continuous steel strip 20 follows travel path 22 throughgalvanizing pot or reservoir 24; Reservoir 24 has walls 26 and containsbath 28 of molten coating metal. The path of travel of the strip isestablished or defined by a sequence of guide rolls around which thestrip is threaded in a conventional manner. The rolls include sink roll30, around which strip 20 passes to change direction. The guide rollsalso include roll 32 which is located in reservoir 24 above sink roll30, and also include roll 34 which is located far above the melt. Thestrip travel path extends through reservoir 24 and through coatingcontrol zone 36, which is positioned above and contiguous to the bath ofmolten coating metal. After passing through coating control zone 36, thestrip changes direction around guide roll 34 and eventually is coiled onmandrel 38 which is driven by variable-speed motor 40 to pull the stripthrough the system.

The strip passing upwardly from the coating bath carries on each of itsbroad, generally planar opposite surfaces a layer or coating of moltencoating metal. In coating control zone 36 are provided nozzles 42, 44which control the shape and thickness of the coatings by wiping excesscoating metal back into the melt. This is effected through means of jetsor barriers of compressed gaseous fluid, in accordance with the basicprinciples taught in the above-referenced Mayhew patent. The jetsimpinge upon the strip at substantially a perpendicular angle, i.e.,from about 5 below the perpendicular to about 10 above, and preferablyat perpendicularity.

Nozzles 42, 44 form part of a coating control rig which includes framemembers 46, 48. The frame members support the nozzles with nozzle 42 onone side of and facing the strip travel path, and with nozzle 44 on theopposite side of and also facing the travel path. Nozzle 42 isapDroximately the same height as nozzle 44. The nozzles are similar toone another, so description of one imparts an Understanding of both.

Nozzle 42 is elongated, and includes upper die member 50 and lower diemember 52 (see also FIG. 3). Since the direction of travel of the stripthrough the coating control zone is upwardly, lower die 52 is upstreamand upper die 50 is downstream relative to the direction of travel ofthe strip. The bottom surface of upper die 50 is flat. An elongatedcavity 54 (FIG. 4) is formed in lower die 52 so that, when the dies areassembled as shown in FIG. 3, the cavity defines an elongated gasmanifold 56. Gas manifold 56 is supplied with compressed gas through aplurality of branch conduits 58 which communicate between nozzlemanifold 56 and gas supply conduit 60 (FIG. 2) which through a flexibleconnection (not shown) communicates with a source of compressed gaswhich can be air, steam or other gaseous fluid, and can be preheated orbe at ambient temperature. Valve 62 is placed in supply conduit 60, forcontrolling the pressure of gas in nozzle manifold 56. The manifold inthe other nozzle has a similar gas supply system.

Upper die 50 and lower die 52 are assembled by bolts (not shown). Holes64 (FIGS. 3, 4) are provided in lower die 52, and tapped holes 66 areprovided in upper die 50, to receive the bolts. An elongated shim 68 isplaced between the rear portions of the dies before assembly to maintainthe front portions of the dies spaced slightly from one another. Withthis arrangement, portion 70 of upper die 50 and portion 72 of lower die52 respectively define top and bottom walls of gas outlet means in theform of a slot or passageway 74. Gas outlet slot 74 faces the strip forpassage of gas out of the nozzle and projection against the strip. Gasoutlet slot 74 extends along a line in a direction which is transverseto the path of travel of the strip. Slot 74 is very small in its widthdimension W (FIG. 3), which is taken in a direction along the travelpath. Shim 68 extends around the ends of the gas manifold in the nozzleand forms end-walls for slot 74 so that gas can escape from the manifoldonly through the gas outlet slot. Slot 74 extends substantially theentire length of the nozzle.

The strip-facing edge of each of dies 50, 52 is rectilinear, andparallel to the surface of the strip. Gas outlet slot 74 extendsoutwardly on each side of the longitudinal centerline of the nozzle toand slightly beyond the edges of the path of travel of the strip. Forany given galvanizing line, the width of the travel path is establishedby the width of the widest strip which is to be processed by the line,plus an additional amount for normal wandering or tracking of the stripto either side of a centered pass line position. Gas outlet slot 74 isconsidered to have an intermediate or central portion 76 (FIGS. 2, whichis centered on the nozzle centerline, and an end portion 78 on each endof intermediate portion 76.

Heating means collectively designated 82 (FIG. 2) are providedcontiguous to gas outlet slot 74 for selectively controlling the width W(FIG. 3) of the gas outlet slot at increments along the length of thegas outlet slot. This is effected through thermal expansion of materialof the walls of the gas outlet slot (principally the upper wall, towhich the heating means is contiguous). Such wall expansion constrictsthe slot and thus reduces the flow of gas from the nozzle.

In the embodiment of FIGS. 1-7, heating means 82 takes the form of aplurality of selectively operable electrical resistanceheating elements84 (FIGS. 3, 6) which are spaced at intervals or increments in adirection along the length of the gas outlet slot. In this embodiment ofthe invention, heating elements 84 are provided at equal intervals allalong the length of the nozzle from one end portion of the gas outletslot to the opposite end portion of the gas outlet slot.

Each heating element 84 includes a U-shaped resistor 86 and a terminal88 and can be of a type such as the Calrod Electrical Heating Elementsmanufactured and sold commercially by the General Electric Company. Eachheating element 84 is received in a separate cavity 90 in upper die 50.Cavities 90 extend from the rear face of the die toward the front of thedie so that the tips of resistors 86 are located at the front endportions of the respective cavities. With this arrangement, heatingelements 84 are in excellent heat exchange relationship with upper wallof gas outlet slot 74 for application of heat to that wall with minimumthermal losses and with maximum thermal expansion of the wall per unitof heat generated by the heating elements. It will be understood thatthe heating elements can be inserted through the top face of the dieinstead of the rear face.

Selective energization of heating elements 84 to heat the top wall ofthe gas outlet slot at the increments of length affected by therespective heating elements to respectively differing temperaturesthereby thermally expands the material of the top wall of the gas outletslot to different degrees and thereby constricts the slot to differentwidths along the length of the slot by, in effect, lowering the top wallof the slot by different amounts. This in turn adjusts the flow of gasthrough the slot at each increment so that the desired wiping action bythe gas jet and thus the desired coating thickness can be obtained ateach increment along the slot length.

For operation of the heating means in the manner just described controlmeans collectively designated 92 (FIG. 8) are provided. The controlmeans includes operating means or control panel structure 94 forselective energization and deenergization of heating elements 84, andincludes the necessary electrical connections between the heatingelements and operating means 94. Operating means 94 is at a locationwhich is spaced remotely from the coating pot and the nozzle structureto make it possible for workmen to manipulate the operating means withfreedom from interruption of coating of the continuous, movingsubstrate. The remote location of the operating means allows it to bemanipulated without interference from the substrate itself, and withoutunsafe or uncomfortable proximity to hot materials. Stated differently,heating elements 84 are operated from a position such that the width ofthe gas outlet slot is under remote control. No interference with, orinterruption of, the process of coating the substrate is necessary, andno unsafe or hot work is required, in order to make coating thicknessadjustments.

The control system for each heating element 84 is like that for each ofthe others, so description of the structure for controlling one heatingelement imparts an understanding of all. In FIG. 8, electrical currentflows from power line 96 and through conductors 98 and 99 to slidingcontact 100, the position of which along resistor 102 is controlled byhandle so that resistor 102 is in effect a variable resistor. Fromresistor 102, current passes through one of the conductors in amulti-conduct'or cable 106 to the leftmost heating element 84 and thecircuit is completed from the heating element through a common groundconductor 108. Movement of sliding contact 100 along resistor 102 byvertical movement of handle 104 changes the amount of heat generated bythe heating element. Since handle 104 is rigidly connected to slidingcontact 100, since conductor 99 is flexible, and since each heatingelement along the length of the gas outlet slot is connected foroperation by a handle 104, the width of the gas outlet slot is displayedall along its length by the position of the handles. Note in FIG. 8 howthe handles define a profile or curve which progressively lowers to theunit centerline on each side, since the sliding contacts 100 areprogressively lower on the resistors in directions approaching thecenterline. With this arrangement of the contacts, the central heatingelements are progressively hotter than those in the end portions indirections to ward the center. Hence, the width of the gas outlet slotin the intermediate portion is constricted, and progressively so,relative to its width in the end portions where less heat is applied andtherefore less thermal expansion takes place. It will be understood thatfinely indexed electrical and electronic display systems can be used inlieu of the handle-positioning system illustrated to display slot width.

Heating elements 84 are received in the upper die in the embodimentillustrated in FIGS. ll-7, but it will be understood that the heatingelements can be placed in either the upper or lower die, or both. Withthe heating elements in the upper die as illustrated, essentially all ofthe thermal expansion is undergone by the upper wall 70 (FIG. 3) of theslot because of the close heat exchange proximity of that wall to theheating elements. Lower wall 72 remains essentially rectilinear or flat.Thus in FIG. 8, the curve depicted by the positions of the handles inessence displays the profile of the upper wall of the gas outlet slot.With heating elements in the lower die in addition to the upper die, thelower wall of the slot also undergoes thermal expansion. And, withheating elements in the lower die only instead of in the upper die, thelower wall of the slot undergoes essentially all of the thermalexpansion and the upper wall of the slot remains essentiallyrectilinear.

In order to enhance the effect of the heating elements in constrictingthe gas outlet slot, upper die 50 is made of material having a highcoefficient of thermal expansion, so that the top wall of the gas outletslot will undergo maximum expansion per unit of heat input. Aluminum isone preferred material for fabrication of the upper die because of itscoefficient of thermal expansion of at least about 1 l X 10' inches perinch per degree Fahrenheit between 32 and 2l2F., see e.g. PerrysChemical Engineers Handbook (fourth Ed.) by John H. Perry et al.,published by McGraw-HilL New York, 1963, page 23-40. As used herein theterm aluminum embraces aluminum-base alloys in addition to the puremetal. Austenitic stainless steels, which have coefficients of thermalexpansion of at least 6 X 10 inches per inch per degree Fahrenheitbetween 32 and 212 F. (Perrys Handbook, pp. 23-35, 23-36), are otherpreferred materials.It is desirable to employ austenitic stainless asthe die material in operations where high temperatures are involved(e.g. where superheated steam is used to form the gaseous barrier), towithstand the high temperatures which are established by the fluids andwhich are required to effect expansion of the top slot wall for controlpurposes. Aluminum is used for low-temperature operations. It will beunderstood that coefficients of thermal expansion vary somewhat withtemperature and coefficients for varying temperatures are published instandard reference works including Aluminum, published by the AmericanSociety for Metals, Metals Park, Ohio, 1967, Vol. I, pp. 280-282 forAluminum, and the Metals Handbook (eighth Ed.) also published by theAmerican Society for Metals, 1961, Vol. I, pp. 422423 for austeniticsteels.

Exemplary slot widths are of the order of about 0.015 inches with thenozzle at ambient temperature. With such widths, the heating elementsneed only have capabilityfor effecting a change in slot width of about0.003 inch, and preferably about 0.005 inch in order to providesatisfactory control. It is desirable to have a gas outlet slot that canbe provided with a 0.005 inch width differential between the endportions and the interme diate portion. The temperatures which arenecessary to produce the requisite expansion will depend upon a numberof variables, including the: operating temperature of the nozzle andincluding the material of the nozzle because as noted above,coefficients of thermal expansion vary among materials, and vary withtemperature within a given material. Die design is also a variable whichmust be considered, because the height of wall determines how muchoverall elongation by thermal expansion the wall will undergo along avertical line, and because not all of the expansion will be in thedesired direction (i.e., downwardly, or into the slot). The die ispreferably designed such that at least one-half of the wall expansion isinto the slot (except in areas contiguous to the end portions of shim60, where expansion of wall 70 is constrained to some extent but notsignificantly detrimentally so because less expansion is needed at theends of the gas outlet slot). The more of the expansion which occurs inthe direction into the slot is the better, from the standpoint ofthermal efficiency. In the embodiment illustrated in FIG. 3, wall 70 hasa height as measured at dimension H of 1 inch. It will be understoodthat heights H of larger values will produce larger absolute values ofexpansion. In order to determine the necessary temperature (over andabove the operating temperature) which is necessary to produce thedesired change in slot width, it is only necessary to determine thenumber of Fahrenheit degrees which are required to elongate wall 70about twice the amount of the desired change in slot width (assumingthat one-half of the expansion will be vertically upwardly, and one-halfvertically downwardly into the slot). This number of degrees iscalculated from the coefficient of thermal expansion for the particularmaterial at the particular temperatures involved, from the particularrequired elongation of the wall, and from the height H of the particularwall.

The nozzle support structure includes a holder ll10 (FIGS. 1, 2) foreach end of each of nozzles 42, 44. Each nozzle holder includes agenerally U-shaped nozzle mounting bracket 112, the back of the bight ofwhich is secured to a rig frame member, as 08. Each bracket 112 includesupper and lower mounting slides 114, 116 respectively and the slides atthe ends of each nozzle define a guideway for the nozzle to move towardand away from the strip travel path. Nozzle 42 is moved along itsguideway to adjust the spacing of the nozzle from the travel path by anadjustment screw 118 at each end of the nozzle. Each screw 118 isrotatably secured to nozzle 42, and is threaded through a stub cylindrical sleeve 120 which is rigidly secured to plate 122 which extendsbetween upper and lower slides 114, 116 of the respective holder 110.Rotation of screw 118 in one direction moves nozzle 42 toward the travelpath, and rotation of screw 118 in the opposite direction moves thenozzle away from the travel path.

Movement of nozzle 44 in its guideways is effected by an adjustmentscrew 124 at each end of the nozzle. Each screw 124 is rotatablyreceived in a fitting 126 which has a projection 128 which extendsdownwardly through a slot 130 formed in the respective upper mountingslide. Each projection 128 is rigidly secured to nozzle 44 and eachscrew 124 is threaded through stub cylindrical sleeve 132 which is fixedto a rig frame member, as 48. Rotation of screws 124 in one directionmoves nozzle 44 toward the strip travel path, and rotation of screws 124in the opposite direction moves the nozzle in the opposite direction,away from the path of travel of the strip.

In one mode of operation of the system thus far described, continuoussteel strip is passed through coating bath 28, and molten coating metaladheres to eachof the opposite surfaces of the strip. The coated stripemerges from the coating bath and passes upwardly into coating controlzone 36 with the coatings still in molten condition. The strip passesbetween coating control nozzles 42, 44 and gas under pressure isprojected from the gas outlet slot of each nozzle against the respectivecoated surface of the strip. The gas projected against the coatedsubstrate controls the molten coating thickness by wiping excess coatingmetal back into the melt in accordance with teachings of the Mayhewpatent. When coating thickness on either coating at any increment acrossthe strip is found to be less than desired, the heating element 84 atthat increment is energized to heat and thereby expand the top wall ofthe gas outlet slot and thereby constrict the gas outlet slot at thatincrement. This decreases the wiping action of the gas jet at thatincrement, resulting in less coating material being wiped back into themelt and thus a thicker coating. It will be understood that it can benecessary to energize a plurality of mutually contiguous heatingelements in order to make the required slot width adjustment, as where,for example, the region of thin coating extends past a plurality ofheating elements. If coating thickness on either coating at anyincrement across the strip is found to be greater than desired, theheating elements of the associated nozzle are energized at allincrements other than the location of the excessively thick coating toconstrict the gas outlet slot at all locations other than that of theexcessively thick coating. The gas pressure, nozzle spacing and/or stripspeed are adjusted in known fashion to bring the wiping action of thegas jet up to the pre-constriction magnitude at all such otherincrements, with the result that the wiping action is increased at theincrement where the slot width was not constricted. The increased wipingaction at this location reduces the thickness of the coating from theexcessive value. As the coating line continues to operate, the thicknessacross the strip is monitored and heating elements selectively energized and/or deenergized as necessary to constrict or increase the widthof the slot to maintain desired coating thickness at all incrementsacross the strip.

Occasionally, as mentioned hereinabove, the coating tends to becomeexcessively thick at the strip edges, forming the so-called heavy edgeand associated problems. To overcome this condition, heating elements 84are selectively energized to progressively constrict the width of thegas outlet slot from the end portions of the gas outlet slot indirections toward the center of the slot in the manner displayed by thehandle positioning of FIG. 8. This technique, when accompanied by anincrease in the gas pressure, nozzle spacing and- /or strip speed tobring the wiping action in the intermediate portion up to itspreconstriction magnitude in order to maintain desired coating thicknessin the center, results in an increased wiping action at the strip edgesand thus a reduction in excessive coating thickness or heavy edge. Infact, if it is not desired to possess capability for incremental controlof the gas outlet slot along the entire length of the slot, the heavyedge problem can be overcome and economies effected by positioningheating elements at increments along only the intermediate portion ofthe gas outlet slot.

In the embodiment of FIGS. 1-7, there are two cooling systems for eachof nozzles 42, 44. Each cooling system is provided for adjustment of thewidth of the gas outlet slot by action in a different way to thermallycontract material of the walls (as with the heating means, principallythe top wall) of the gas outlet slot. These cooling systems aregenerally designated 134 and 136 in FIGS. 5, 6, and 7. Cooling system134 includes passage 138 (FIGS. 5, 7) for a coolant fluid, e.g. water.Passage 138 extends from one end portion to the other end portion of thegas outlet slot in close heat exchange relationship to top wall 70. Acoolant fluid inlet passage in the form of a conduit 140 which iscontrolled by a valve 142 is provided at one end portion of passage 138,and a coolant fluid outlet passage in the form of a conduit 144 (FIG. 2)is provided at the other end portion. By opening inlet valve 142 (FIG.7) and passing coolant fluid through passage 138, preferably with theheating elements deenergized, the top wall of the gas outlet slot can bethermally contracted in rapid fashion. This is advantageously done,e.g., when it is desired to make a general change in slot profile, sincethe thermal contraction of the top wall which is caused by cooling allalong the slot causes the width of the slot to increase toward valuesextant before constriction by thermal expansion, i.e., toward therectilinear shape which the top wall possesses at ambient temperature.This in effect erases the profile of the top wall which is provided by aparticular pattern of energization of the heating elements so that a newprofile produced by a new pattern of heating element energization can beinstituted. Or, cooling of the die by cooling system 134 can be used todislodge specks of scale or other foreign matter which can become stuckin the gas outlet slot. Cooling system 134 can be used for this latteror any other desired purpose by itself without any heating elements inthe die and/or without the presence of cooling system 136.

Cooling system 136 (FIGS. 5, 6) includes a coolant fluid passage 146which extends along each end portion 78 of the gas outlet slot. A secondpassage 148 controlled by a valve 150 is provided at the outer endregion of each passage 146 for inlet of coolant fluid. Passage 146 doesnot extend completely through the die but rather, terminates in theintermediate portion of the die. A plurality of spaced-apart fluidoutlet passages 152, 154, 156 are provided along each passage 146.Valves 158, 160 are provided for controlling flow through outletpassages 154, 156.

With cooling system 136, cooling can be employed to aid the heatingelements in production of a larger temperature differential between endportions and intermediate portion of the gas outlet slot than can beprovided by heating elements alone. In this mode, the heating elementsin the intermediate portion are energized to provide high temperaturesand the heating elements in the end portions are energized for lowtemperature or deenergized, and the transition heating elements betweenthese extremes are energized to progressively move from one to theother. With valves 158, 160 at each end open and with water circulatingthrough each passage 146, cooling of the maximum length of the gasoutlet slot is achieved. By throttling each valve 160 to minimize flowthrough the associated outlet passage 156, cooling along a lesser lengthof the gas outlet slot is effected, and similarly, throttling each valve158 decreases cooling along a still longer length of the slot. Careshould be taken not to completely close valves 160 or valves 158 so asto permit escape of vaporized coolant liquid entrapped upstream of therespective valves.

It will be appreciated that if desired either or both of cooling systems134, 136 can be dispensed with and heating means alone used to controlthe width of the gas outlet slot. It will further be appreciated that,as with the heating means, the cooling means can be used in the lowerdie in addition to or in lieu of the upper die.

It has been said herein above that the heating elements are spaced atincrements along the gas outlet slot, and an example of spacing for theheating ele ments is on one-inch centerlines. This provides a controlsystem having capability for fine adjustments along the length of thegas outlet slot. However, where less precise control is acceptable,larger spacings (e.g., 2 inches or 3 inches) can be used. And, where itis not desired to have equal selectivity all the way across the stripbut it is desired to have capability for producing greater constrictionin the intermediate portion of the gas outlet slot than in the endportions, the heating elements can be spaced at closer increments alongthe intermediate portion of the gas outlet slot than along the endportions. Such a construction is illustrated in the embodiment of FIG.9. Also in FIG. 9 is depicted a slightly different form of coolingsystem which combines capabilities of the two cooling systems of FIGS.5-7, along with a further modification in which flexibility for coolingalong the length of the slot is somewhat reduced. In FIG. 9, anadditional passage 162 is provided to connect the two passages 146A.Also, a twoway valve 164 is provided at one end of the nozzle forselective connection of right-side passage 146A with a coolant fluidsupply conduit 166 or a coolant fluid discharge conduit 168. In one modeof operation, valve 164 is operated to connect supply conduit 166 torightside passage 146A and valve 150A is opened to admit coolant fluidto left-side passage 146A and the two end portions of the gas outletslot are cooled in the manner discussed in connection with the coolingsystem of FIG. 5. Coolant vapor generated in stagnant-flow centralpassage 162 escapes through outlet conduits 152A, 154A. In another modeof operation, each valve 158A is throttled down to eliminate liquid flowto the extent possible while allowing for escape of entrapped vapor, andreduce the length of slot which is cooled.

In still another mode of operation, all of valves 158A and 176 arethrottled down to eliminate liquid flow to the extent possible whileallowing for escape of vapor. Valve 164 is switched to communicateright-side passage 146A with coolant discharge conduit 168. Coolantfluid passes from inlet valve A through the entire length of the die andis discharged through conduit 168 to erase the existing slot profile, todislodge a foreign particle, or for other purposes as discussed above inconnection with the cooling system of FIG. 7.

All valves herein disclosed are solenoid-operated and controlled in aconventional manner from the remote control panel at which is locatedthe operating structure for the heating means.

If desired, and if the great flexibility of control which is provided byindividual heating elements is not required, a capability for producinga higher temperature in the intermediate portion of the gas outlet slotthan in the end portions can be realized by heating means such asdepicted in the embodiments of FIGS. 10 and 11. In these embodiments,the heatingmeans take the form of elongated electrical resistors whichextend along the respective gas outlet slots and which have greaterelectrical resistance in the intermediate por tions than in the endportions so as to produce progressively high temperatures (and thereforeprogressively constrict the slot) inwardly on each side toward thecenter. In FIG. 10, the heating means takes the form of a wound nichromeribbon 172 having progressively increasing numbers of turns as itapproaches the center of the gas outlet slot from each side, so that theelectrical resistance of the ribbon is greatest in the intermediateportion of the gas outlet slot. It will be understood that, instead ofincreasing the number of turns, progressively increasing the thicknessof the ribbon in the intermediate portion could achieve the same result.Also, a wire could be used in lieu of a ribbon. With the form of heatingmeans illustrated in FIG. 10, passage of current of different valuesthrough the heating means produces different temperatures at incrementsalong the length of the gas outlet slot in accordance with the differentvalues of electrical resistance along the length of the heating meansand with the value of the current passed through.

In FIG. 11, the heating means takes the form of a plurality ofelectrical resistors 174 which are elongated and extend in a directionalong the length of the gas outlet slot. Resistors 174 progressivelydecrease in length so that the resistance of the heating meansconsidered as a whole is greatest in the intermediate portion of the gasoutlet slot. Resistors 174 can be individually or gang-controlled, withindividual control increasing the flexibility of the heating means withrespect to providing given temperatures at particular increments alongthe length of the gas outlet slot.

FIG. 12 depicts still another embodiment of the invention which employsan automatic control system for the heating means. In this embodiment,the control means includes sensing means in the form of a thermocouple176 for selectively detecting the temperature at the walls of the gasoutlet slot at each increment along the length of the gas outlet slot.The control means also includes a controller 178 which is responsive toeach thermocouple for selectively actuating the heating element 84Dwhich is associated with the respective thermocouple to maintain atemperature which is preset on the controller for each increment alongthe die. It will be appreciated that there is a thermocouple 176 at eachheating element 84D along the die length. Thermocouples 176 can also beused to record the slot profile, because temperature is related to thesize of the slot. Note also that the embodiment of FIG. 12 includes onlyone cooling system, which corresponds to that designated 136 in FIG. 5.

FIG. 13 depicts another form of heating element 179, which is similar tothat of the embodiment of FIGS. 1-7 but which has a resistor 180 ofgreater effective length, for production of more heat. The resistor isfolded upon itself, for compactness.

Operations in accordance with the invention are highly advantageous.Coating thickness can be controlled at increments across the width ofthe strip so that the coating thickness is as desired at all incrementsacross the strip. Uniform coating thickness can be provided if desired,or the coating can be shaped to be thinner at the edges than at thecenter to facilitate coiling, if that is desired. In any event, heavyedge and resultant spooled coils can be avoided, as can coatings withundesired thin or thick areas.

Control over the coating thickness effected by control over the width ofthe gas outlet slot in accordance with the invention is effectedinstantaneously, with only the labor required to adjust the heatercontrols and with absolute comfort and safety. No interruption ofcoating or downtime on the coating line is required. Further, cooling inaccordance with the teachings of the invention makes it possible torapidly change die profile, to dislodge foreign objects, and to maintainhigh temperature differentials between end portions and intermediateportion of the gas outlet slot.

The invention has been described in connection with embodiment of itsprinciples in a galvanizing environment. However, the coating need notbe zinc; other materials, metals and nonmetals, can be applied. And thesubstrate need not be steel or even metallic; other materials, e.g.paper, can be coated. Further, control of flow of fluids through slotsor other passageways in other than coating environments canadvantageously be had with use of thermal expansion and/or contractionprinciples of the invention. Accordingly, for definition of theprinciples and the scope of the invention, reference will be made to theappended claims.

I claim:

1. Coating control apparatus, comprising elongated nozzle means forprojecting a gaseous barrier against a coated surface of a continuoussubstrate to wipe excess molten coating material from the continuoussubstrate to control the thickness of molten coating on the surface ofthe continuous substrate,

the nozzle means including walls defining linearly extended gas outletmeans for projecting gas from the nozzle means,

the gas outlet means having length in a direction along the nozzlemeans,

the gas outlet means having width in a direction transverse to thelength and transverse to the direction of projection of gas from thenozzle means,

heating means contiguous to the gas outlet means for controlling thewidth of the gas outlet means by thermally expanding at least a portionof the walls of the gas outlet means, and

control means for the heating means,

the control means including means for operating the heating means from alocation spaced remotely from the nozzle means.

2. Apparatus as defined in claim 1,

in which the heating means includes means for selectively controllingthe width of the gas outlet means at increments in a direction along thelength of the gas outlet means.

3. Apparatus as defined in claim 1,

the heating means including a plurality of spacedapart, selectivelyoperable heating elements.

4. Apparatus as defined in claim 1,

the heating means being electrical heating means.

5. Apparatus as defined in claim 1,

at least the portion of the walls of the gas outlet means being ofhighly expansible material having a coefficient of thermal expansion ofat least about 6 X 10 inches per inch per degree Fahrenheit between 32and 212 F.

6. Apparatus as defined in claim 5,

the nozzle means including a pair of die members,

one of the die members being of the highly expansible material,

the heating means being mounted on the one die member.

7. Apparatus as defined in claim 1, including cooling means contiguousto the gas outlet means for adjusting the width of the gas outlet meansby thermally contracting at least a portion of the walls of the gasoutlet means.

8. Apparatus as defined in claim 7,

the cooling means including coolant fluid passage means in the nozzlemeans.

9. Coating process, comprising the steps of passing a continuoussubstrate having opposite surfaces along a travel path through a bath ofcoating material to form a coating on at least one of the surfaces ofthe substrate,

passing the coating substrate through a coating control zone contiguousto the bath,

providing nozzle means in the coating control zone for controlling thethickness of the coating on at least the one surface of the substrate,

each nozzle means including walls defining linearly extended gas outletmeans,

the gas outlet means having length in a direction transverse to thetravel path,

the gas outlet means having width in a direction along the travel path,

projecting a gaseous barrier under pressure from the gas outlet meansagainst the coated substrate to wipe excess coating material into thebath, and

controlling the width of the gas outlet means by thermally changing thevolume of at least a portion of the walls of the gas outlet means,

thereby controlling the flow of gas through the gas outlet means.

10. The process of claim 9,

in which the volume is thermally changed by heating.

13. The process of claim 9,

in which the volume is thermally changed at increments in a directionalong the length of the gas outlet means.

1. Coating control apparatus, comprising elongated nozzle means forprojecting a gaseous barrier against a coated surface of a continuoussubstrate to wipe excess molten coating material from the continuoussubstrate to control the thickness of molten coating on the surface ofthe continuous substrate, the nozzle means including walls defininglinearly extended gas outlet means for projecting gas from the nozzlemeans, the gas outlet means having length in a direction along thenozzle means, the gas outlet means having width in a directiontransverse to the length and transverse to the direction of projectionof gas from the nozzle means, heating means contiguous to the gas outletmeans for controlling the width of the gas outlet means by thermallyexpanding at least a portion of the walls of the gas outlet means, andcontrol means for the heating means, the control means including meansfor operating the heating means from a location spaced remotely from thenozzle means.
 2. Apparatus as defined in claim 1, in which the heatingmeans includes means for selectively controlling the width of the gasoutlet means at increments in a direction along the length of the gasoutlet means.
 3. Apparatus as defined in claim 1, the heating meansincluding a plurality of spaced-apart, selectively operable heatingelements.
 4. Apparatus as defined in claim 1, the heating means beingelectrical heating means.
 5. Apparatus as defined in claim 1, at leastthe portion of the walls of the gas outlet means being of highlyexpansible material having a coefficient of thermal expansion of atleast about 6 X 10 6 inches per inch per degree Fahrenheit between 32*and 212* F.
 6. Apparatus as defined in claim 5, the nozzle meansincluding a pair of die members, one of the die members being of thehighly expansible material, the heating means being mounted on the onedie member.
 7. Apparatus as defined in claim 1, including cooling meanscontiguous to the gas outlet means for adjusting the width of the gasoutlet means by thermally contracting at least a portion of the walls ofthe gas outlet means.
 8. Apparatus as defined in claim 7, the coolingmeans including coolant fluid passage means in the nozzle means. 9.Coating process, comprising the steps of passing a continuous substratehaving opposite surfaces along a travel path through a bath of coatingmaterial to form a coating on at least one of the surfaces of thesubstrate, passing the coating substrate through a coating control zonecontiguous to the bath, providing nozzle means in the coating controlzone for controlling the thickness of the coating on at least the onesurface of the substrate, each nozzle means including walls defininglinearly extended gas outlet means, the gas outlet means having lengthin a direction transverse to the travel path, the gas outlet meanshaving width in a direction along the travel path, projecting a gaseousbarrier under pressure from the gas outlet means against the coatedsubstrate to wipe excess coating material into the bath, and controllingthe width of the gas outlet means by thermally changing the volume of atleast a portion of the walls of the gas outlet means, therebycontrolling the flow of gas through the gas outlet means.
 10. Theprocess of claim 9, in which the volume is thermally changed by heating.11. The process of claim 10, in which the volume is also thermallychanged by cooling.
 12. The process of claim 9, in which the volume isthermally changed by cooling.
 13. The process of claim 9, in which thevolume is thermally changed at increments in a direction along thelength of the gas outlet means.